1. Field of the Invention
The invention relates to the manufacture of mufflers for the exhaust systems of internal combustion engines using flexible fibrous muffler packing material, preferably long or continuous strand fiberglass. Such fiberglass is preliminarily packed into transfer containers or cartridges for shipping, using a discharge apparatus that fluffs and separates individual filaments from multi-filament continuous strands fed from spools. The packing is ejected from the cartridge at the muffler manufacturing site, into a preformed muffler housing, using a piston or pusher with tines extending through the rear of the cartridge. The packing is compressed and confined in the muffler housing by insertion at the end of the piston stroke of an end seal of preformed packing carried in the cartridge. The cartridges can be disposable but preferably are reusable.
2. Prior Art
Exhaust mufflers, resonators and similar devices (herein collectively termed mufflers) mute the noise produced by the cylinders of an internal combustion engine and can adjust the sound emitted by the engine, according to the "tune" of the muffler. A muffler housing mounted in series with the exhaust flow path defines one or more passageways that communicate via perforations, slots or other openings with internal chambers within the muffler housing. Some of the chambers can be hollow and shaped to obtain a particular resonant effect, but at least one of the chambers to which the exhaust gases are exposed typically is packed with a sound absorbing fibrous muffler packing. In a simple example, a cylindrical external muffler housing surrounds a perforated coaxial through-tube, and the packing is placed in a space between the perforated tube and the external housing. In other examples the flowpath of all or part of the gas is directed through a mass of muffler packing. In any event, as the exhaust passes through the muffler, sound waves vibrate the packing material and are partly absorbed.
There are two basic ways to install the muffler packing. A molded body of packing material having a shape that conforms to the cavity can be made and inserted as a preformed substantially rigid unit. Alternatively, the muffler can be loaded with loose fiber material that is then compressed by the internal and external walls of the muffler to reside in the necessary chambers.
In the case of a molded body of packing, fibers of fiberglass, mineral wool (e.g., basalt) or the like are mixed with a resin and molded to the required shape by curing the resin chemically or with heat. This technique has the benefit that the packing can be handled as a unit, and installation involves simply placing the packing body into position in the housing during assembly. However there are also drawbacks. The resin which holds the shape of the packing burns away over an initial period of use of the muffler. Exhaust from a new muffler may contain smoke from burning resin, or at least may smell noticeably. The presence of the resin also affects the sound or tune of the muffler, which causes the sound of the engine to change as the resin is burned off. Assuming that the muffler is designed for optimal sound in the long run (i.e., after the resin burns off), the sound of a new muffler is relatively inferior.
Mufflers are made in various shapes, sizes and structures. In addition to the familiar cylindrical and oval-cross section configurations, for example, stamped plate mufflers are known wherein flow paths and chambers are defined between formed plates. The chambers in these mufflers are readily capable of various shapes and sizes. Each distinct size and shape requires a corresponding molding apparatus for forming the muffler packing, which can be expensive.
A further drawback of rigidly molded packing is that manufacturing variations occur in dimensions such as width, length, out-of-round and the like, both in the packing body and in supposedly-complementary muffler housings. It is desirable that the packing fit snugly into the cavity provided for it, filling the cavity completely and obstructing possible bypass passages around the packing. However to ensure that the relatively incompressible molded packing will fit easily into place, the body of packing material is generally sized slightly smaller than the cavity. In this way a packing body that is oversized compared to nominal and/or a muffler housing that is undersized, still can be accommodated. This often results in bypass spaces and looseness of the fit.
Dimensional tolerance is not a problem with directly packed loose fibers, because they flexibly conform to the size of the cavity in which they are placed and are generally compressed during installation. Nor do loose fibers have a problem with burning resin. However, loose fibers can be difficult to handle. Loose fibers can become lodged in seams between structural parts of the muffler if assembly includes compressing the fibers between the structural parts. Loose fibers are also difficult to confine in a gas flow path.
Conventional fiberglass as used for much acoustic and thermal insulation consists of short fibers interleaved with one another forming a batt. Short fiber material is often uncomfortable to handle and may cause a scratchy or itchy feeling when the fibers and associated dust are allowed to contact the skin.
Fiberglass fibers can be produced in indefinitely long lengths, and used to weave or knit textiles. It is also known to use long fibers for thermal insulation to address the scratch/itch disadvantage of short fiber batts. When used for insulation the material is sometimes referred to as "continuous" fiber fiberglass. The material is produced initially as a textile material in that during production, glass fibers are collected and are wound on spools in the form of strands or yarns, each having a plurality of coextensive single fibers. The individual fibers can be adhered in the yarn using sizing. Such a material is available, for example, from Owens Corning Fiberglas Corp., Toledo, Ohio, under the trademark Advantex. This textile-like spooled material can be fluffed and separated into generally randomly oriented individual fibers that are each quite long, using equipment that is also available from Owens Corning Fiberglas.
The strands of parallel fibers are fed from the spools to a pneumatic dispensing head having a vortex or venturi structure that swirls compressed air together with the fibers as they are fed along a discharge path. The fibers are whipped, spun and separated by action of the swirling compressed air. The dispensing head discharges an air-impelled stream of loose fibers. The form of the fibers, namely separated and randomly crossed in a volume, is appropriate for use as insulation, muffler packing or the like. The total fiber length and corresponding volume can be closely controlled by metering the length of strand discharged.
Handling continuous strand fluffed fiberglass is not uncomfortable due to scratching and itching problems, but the fluffed material is loose and flowable. Therefore, manipulating a mass of the loose fibers is awkward and inconvenient. It is particularly awkward to stuff a mass of loose fibers into a cavity, to distribute, compress and confine the fibers in the cavity, and to close off the cavity with an end wall or the like without some fibers interfering with the seam between the cavity and end walls. It would be advantageous, rather than stuffing the cavity, to use the capability of a pneumatic dispensing head or the like as described above, at least for discharging fluffed fibers directly into the muffler housings where they are to be confined. The intensity of the stream of air impelling the fluffed fibers can be controlled to control packing density, and the discharge direction oriented as needed to flow and distribute the material into the cavity.
However, obtaining, operating and maintaining a fiber injection production line may entail a cost of some hundreds of thousand dollars. This expense is not justified in a typical muffler production factory. If loose continuous fiber fiberglass is to be otherwise provided to muffler producers by suppliers of fiber or insulation products, it must be packaged. The material could be transferred from a bulk package to the muffler manually, but this is awkward. Alternatively, a plastic or paper bag or similar enclosure can be provided to be installed directly in the muffler cavity, as a shaped resilient body which is compressed into the cavity and at least confines the fibers. This has many of the same drawbacks as resin preformed rigid molded packing. The package material must be burned away in use, thereby altering the muffler tune over time and causing smoke and/or odor.
In commonly owned patent application Ser. No. 08/975,910, filed Nov. 21, 1997, entitled Muffler Packing Method and Apparatus, continuous strand fiberglass is provided in a shaped bag made of an open mesh plastic or fiberglass. The mesh bag avoids the problem of alteration of the muffler's tune and minimizes any smoke or odor because the mesh contains relatively little combustible material. However, such packaging bags present an additional expense in material and manufacturing, and it would be advantageous if the benefits of a package could be obtained without the corresponding drawbacks.